Multi layered felt, member formed of same, and method of manufacturing same

ABSTRACT

To provide various members such as filter cloth for dust collection which assures small pressure loss and easy shaking down of dust particles and is excellent in friction property and mechanical strength, sliding member excellent in sliding property, water repellent member excellent in water repellency, non-sticking member excellent in non-sticking property and member for supplying mold releasing agent in electrophotographic apparatuses which is excellent in air permeability, heat resistance and oil resistance, and provide a multilayered felt used therefor and a process for producing the multilayered felt. The multilayered felt is obtained by placing a layer of a web comprising polytetrafluoroethylene staple fibers on at least one surface of a felt and then joining the polytetrafluoroethylene staple fibers and fibers which form the felt by intermingling through water jet needling and/or needle punching.

TECHNICAL FIELD

The present invention relates to a multilayered felt produced by forminga layer of polytetrafluoroethylene (PTFE) staple fibers havingintermingling property on at least one surface of a felt, and a processfor producing the multilayered felt. More particularly the presentinvention relates to members produced from the above-mentionedmultilayered felt, namely, a sliding member, water repellent member,non-sticking member, member for supplying mold releasing agent inelectrophotographic apparatuses and filter cloth for dust collection.

BACKGROUND ART

In recent years almost all kinds of fibers have been processed byvarious methods to produce felts.

Examples of the fiber are, for instance, staple fibers of polyester,meta-linked aramid, para-linked aramid, polyphenylene sulfide (PPS),polyimide and the like. The felts are produced by placing a web obtainedfrom the mentioned staple fibers on one side of a base fabric such as aplain-woven fabric made from monofilaments, multifilaments or processedyarns of the respective fiber or sandwiching the base fabric with thewebs and then, needle-punching. Those felts are used in many industrialfields, for example, for applications such as sliding member, waterrepellent member, non-sticking member, member for supplying moldreleasing agent in electrophotographic apparatuses and filter cloth fordust collection.

Particularly when the felts are used for filter clothes for dustcollection, as compared with woven fabrics having the same dustcollecting efficiency, the felt has a surface porosity of about twotimes, and there is a merit such that air permeability per unitfiltrating area becomes two times and pressure loss is small and powerconsumption for air blasting is small. On the other hand, in case of thefilter cloth for dust collection which is produced from a felt obtainedby simple needling of the above-mentioned staple fibers, there is aproblem that a part of particles to be removed enters inside of the feltduring use, which causes blockage of the felt and increase in pressureloss. Also there is a problem that shaking down of adhered andaccumulated particles on the surface of the felt are insufficient.

In order to solve these problems, with respect to felts used for filterclothes for dust collection such as felts for bag filter, variousmethods for improvements mentioned below have been proposed.

(1) A method in which fluffy fibers existing on a dust-collectingsurface of the felt are minimized by singeing the fluffs with a burneror calendering the surface of the felt at a temperature close to itssoftening temperature;

(2) A method in which needle punching is carried out to increase adensity of a dust-collecting surface of the felt;

(3) A method in which a filter cloth for dust collection obtained bylaminating a non-woven fabric sheet on a surface of a needled felt isused in order to reduce blockage while maintaining strength and form ofthe felt, the method being disclosed in JP-A-3-60712;

(4) A method in which a dispersion containing PTFE particles is appliedon a dust-collecting surface of the felt, followed by fusing: and

(5) A method in which a porous PTFE film is laminated on adust-collecting surface of the felt with an adhesive.

However in the above method (1), dust particles accumulated on thedust-collecting surface of the felt become easy to be shaken down to acertain extent but it is not enough. In the above methods (2) and (3), adensity of the dust-collecting surface of the felt increases(densification of surface), entering of dust particles into the insideof the felt can be prevented and the dust particles become easy to beshaken down, but the methods are still not satisfactory.

In the above method (4), since expensive PTFE is used only on thesurface of the felt, it is advantageous from the viewpoint of cost. Alsothough shaking down of the dust particles becomes easy because ofnon-sticking property which PTFE possesses, a coating film of PTFE iseasy to be separated and is inferior in friction property. Further inorder to form the PTFE coating film, it is necessary to sinter at hightemperature and thus, heat resistance is required for fibers which formthe felt. Accordingly there is a problem that kind of fibers to be usedis limited.

In the above method (5), there are the same merits as in the abovemethod (4). However, since the adhesive is used, there is a problem thata porosity of the felt decreases and a pressure loss increases.

The above methods (1) to (5) direct to improvements in entering of dustparticles and shaking down of the particles by densification andmultilayered construction of the felt, but are not satisfactory becausethose methods have the mentioned problems as it is clear from theresults obtained from microscopic observation of sectional view ofdust-collecting surface of the felt.

An object of the present invention is to provide various members such asa filter cloth for dust collection which has small pressure loss,assures easy shaking down of dust particles and is excellent in frictionproperty and mechanical strength; a sliding member having excellentsliding property; a water repellent member having excellent waterrepellency; a non-sticking member having excellent non-stickingproperty; and a member for supplying mold releasing agent inelectrophotographic apparatuses which is excellent in air permeability,heat resistance and oil resistance, and to provide a multilayered feltused therefor and a process for producing the felt.

DISCLOSURE OF THE INVENTION

The present invention relates to a multilayered felt obtained by forminga layer of a web comprising PTFE staple fibers on at least one surfaceof a felt and joining the PTFE staple fibers and fibers which form thefelt by intermingling.

In the present invention, it is preferable that the PTFE staple fibershave a branch and/or a loop.

In the present invention, it is further preferable that a fiber lengthof the PTFE staple fibers is from 3 to 25 mm.

In the present invention, it is further preferable that theabove-mentioned PTFE comprises a semi-sintered PTFE.

In the present invention, it is further preferable that a weight of aweb comprising the above-mentioned PTFE staple fibers is from 50 to 500g/m².

The present invention further relates to a sliding member comprising anyone of the above-mentioned multilayered felts.

The present invention further relates to a water repellent membercomprising any one of the above-mentioned multilayered felts.

The present invention further relates to a non-sticking membercomprising any one of the above-mentioned multilayered felts.

The present invention further relates to a member for supplying moldreleasing agent in electrophotographic apparatuses comprising any one ofthe above-mentioned multilayered felts.

The present invention further relates to a filter cloth for dustcollection comprising any one of the above-mentioned multilayered felts.

In the present invention, it is preferable that the fibers which formthe felt are at least one selected from the group consisting ofpolyester fibers, meta-linked aramid fibers, para-linked aramid fibers,polyphenylene sulfide fibers, polyimide fibers, phenol resin fibers,fluorine-containing resin fibers, carbon fibers or glass fibers.

The present invention further relates to a process for producing amultilayered felt by placing a web of PTFE staple fibers on at least onesurface of a felt and then joining the PTFE staple fibers and the fiberswhich form the felt by intermingling through water jet needling and/orneedle punching.

In the present invention, it is preferable that the PTFE staple fibersare obtained by tearing and opening a uniaxially stretched PTFE filmwith a needle blade roll rotating at high speed and that immediatelyafter the opening, the PTFE staple fibers are accumulated on the felt tobe joined to form the web.

In the present invention, it is preferable that the PTFE staple fiberswhich form the web are previously subjected to hydrophilization and thatimmediately after the opening, the PTFE staple fibers are accumulated onthe felt to be joined to form the web.

In the present invention, it is preferable that the web is joined to thefelt after being subjected to hydrophilization.

In the present invention, it is preferable that the web is subjected tohydrophilization with a hydrophilic liquid having a surface tension ofnot more than 30 dyne/cm.

In the present invention, it is preferable that the above-mentioned PTFEcomprises a semi-sintered PTFE.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is explanatory cross-sectional views of a filter cloth for dustcollection obtained from the multilayered felt of the present invention,and (a) represents a view before dust collection and (b) represents aview after dust collection.

FIG. 2 is an explanatory cross-sectional view of an equipment fortearing and opening a uniaxially stretched PTFE film.

FIG. 3 is explanatory views of a PTFE staple fiber having loop and/orbranch structure and good crimping property.

FIG. 4 is an explanatory cross-sectional view of a pair of upper andlower needle blade rolls for splitting a uniaxially stretched PTFE film.

FIG. 5 is an explanatory plan view of a PTFE film punched with needlesof the needle blade rolls of FIG. 4.

FIG. 6 is an explanatory cross-sectional view of an angle of the needleof the needle blade roll of FIG. 4 to the PTFE film.

FIG. 7 is an explanatory cross-sectional view of a carding machine forobtaining cotton-like material.

FIG. 8 is explanatory views showing a cross-sectional view (a) and aplan view (b) of the needle blade roll of the tearing and openingequipment of FIG. 2.

FIG. 9 is an explanatory cross-sectional view of an equipment forevaluating performance of a filter cloth for dust collection.

FIG. 10 is a graph showing pressure loss of filter clothes for dustcollection which are produced from each felt of Example 1 andComparative Example 2.

FIG. 11 is explanatory cross-sectional views of a filter cloth for dustcollection obtained in Comparative Example 2, and (a) represents a viewbefore dust collection and (b) represents a view after dust collection.

FIG. 12 is an explanatory cross-sectional view of an equipment fortearing and opening a PTFE film, accumulating the film on a base feltand then intermingling fibers.

BEST MODE FOR CARRYING OUT THE INVENTION

The major feature of the multilayered felt of the present invention isthat at least one of the surfaces of a felt (hereinafter referred to as"base felt") is joined with a web comprising PTFE staple fibers,particularly PTFE staple fibers having a branch and/or a loop and thatthe staple fibers are, by making the use of their interminglingproperty, joined with the base felt-forming fibers, particularly thefibers around the neighborhood of the surface of the base felt. Thisassures excellent friction property and makes it possible to use themultilayered felt for various members.

In the present invention, according to the multilayered construction, aninterface between the felt layer and the web layer of PTFE staple fibersmay not be necessarily clear, and the multilayered construction meansthat a layer which is rich in the felt-forming fibers and a layer whichis rich in the staple fibers are joined together. The surface of thefelt may have the joined web incontinuously. For example, there arecases where the PTFE staple fibers are pressed into the felt layer byneedle punching and on the contrary, the fibers of the felt are pulledout of the surface of the web layer of PTFE staple fibers. A ratio ofsuch an incontinuous portion on the surface can be selected depending onapplications of the felt.

The base felt which can be used in the present invention is obtainedfrom usual fibers by known methods, for example, by needle punching, andcommercially available felts can be used.

Examples of the base felt-forming fiber are, for instance, animal fiberssuch as wool; vegetable fibers such as cotton; inorganic fibers such ascarbon fiber and glass fiber; organic synthetic fibers such as polyesterfiber, meta-linked aramid fiber, para-linked aramid fiber, polyphenylenesulfide (PPS) fiber, polyimide fiber, phenol resin fiber,fluorine-containing resin fibers including sintered PTFE fiber andmelt-spinning fiber such as tetrafluoroethylene-hexafluoropropylenecopolymer fiber, tetrafluoroethylene-perfluoro(alkyl vinyl ether)copolymer fiber or ethylene-tetrafluoroethylene copolymer fiber,polyolefin fibers such as polyethylene fiber and polypropylene fiber,acrylic fiber and nylon fiber; and the like. Among them, in case of afilter cloth for dust collection, one or a mixture of two or more ofpolyester fiber, meta-linked aramid fiber, para-linked aramid fiber,polyphenylene sulfide fiber, polyimide fiber, phenol resin fiber,fluorine-containing resin fiber, carbon fiber and glass fiber ispreferable.

In the center region of the base felt is preferably used a base fabriccomprising a woven fabric obtained by plain weaving, etc. from theviewpoint of improvement of strength. Examples of the preferred fibersused for the base fabric are the fibers mentioned above.

Examples of the PTFE staple fiber used in the present invention are, forinstance, a fiber obtained from an aqueous dispersion prepared byemulsion polymerization of tetrafluoroethylene (TFE) throughemulsion-spinning step and sintering step; a fiber obtained from a PTFEfilm through sintering step, slitting step, stretching step, etc.; afiber obtained from a PTFE film through sintering step, stretching step,tearing step, etc.; a fiber obtained from a PTFE film through sinteringstep, stretching step, splitting step, cutting step, etc.; and the like.

From the viewpoint of excellent intermingling property and property forpreventing falling off of fibers, preferable is a staple fiber obtainedfrom a PTFE film through sintering or semi-sintering step, stretchingstep, tearing and opening steps by a needle blade roll rotating at highspeed, etc., because the fiber has a branch and/or a loop.

Further, a staple fiber obtained through semi-sintering step ispreferable from the points that since the fiber having a largestretching ratio (3 to 6 times that of a fiber obtained through asintering step) and a small specific gravity can be obtained, a weightof a web can be made smaller and that since a self-sticking property iseasy to be exhibited, fluffing can be reduced by heat pressing andsmoothness is excellent.

In the present invention, the PTFE staple fibers can be used incombination with other fibers, for example, inorganic fibers, heatresistant synthetic fibers, fluorine-containing resin fibers, polyolefinfibers, polyester fibers or natural fibers or a mixture of two or morethereof.

A mixing ratio of the other fibers is from 10 to 90% by weight,preferably from 10 to 75% by weight, more preferably from 15 to 75% byweight. When the mixing ratio is less than 10% by weight, there is atendency that intermingling property is not improved and the otherfibers become merely impurities. When more than 90% by weight, there isa tendency that characteristics of PTFE are not exhibited.

The purpose of using two or more of other fibers is to produce amultilayered felt suitable for its final application by changingcharacteristics such as intermingling strength, apparent density and airpermeability of the multilayered felt and giving electric conductivityto the felt.

Examples of the inorganic fiber are, for instance, carbon fiber, glassfiber, metal fiber, asbestos, rock wool, etc. From the viewpoint offiber length, carbon fiber, glass fiber and metal fiber are preferred.

Examples of the metal fiber are, for instance, stainless steel fiber,copper fiber, steel fiber, etc. From the viewpoint of corrosionresistance, a stainless steel fiber is preferred.

Examples of the preferred heat resistant synthetic fiber are, forinstance, polyphenylene sulfide (PPS) fiber, polyimide (PI) fiber,para-linked aramid fiber, meta-linked aramid fiber, phenol resin fiber,polyarylate fiber, carbonated fiber, fluorine-containing resin fiber,etc.

Examples of the preferred fluorine-containing resin fiber are, forinstance, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer(PFA) fiber, tetrafluoroethylene-hexafluoropropylene copolymer (FEP)fiber, ethylene-tetrafluoroethylene copolymer (ETFE) fiber, polyvinylfluoride (PVF) fiber, polyvinylidene fluoride (PVdF) fiber,polychlorotrifluoroethylene (PCTFE) fiber,ethylene-chlorotrifluoroethylene copolymer (ECTFE) fiber, etc.

Examples of the preferred polyolefin fiber are, for instance,polyethylene fiber, polypropylene fiber, etc. From the viewpoint ofpurity, polyethylene fiber and polypropylene fiber are preferable.

Examples of the polyester fiber are, for instance,polyethyleneterephthalate fiber, polybutyleneterephthalate fiber, etc.From economical point of view for production in industrial scale,polyethyleneterephthalate fiber is preferable.

In addition, for example, nylon fiber, urethane fiber, etc. can be used.

Examples of the natural fiber are, for instance, wool, cotton, cashmere,angola rabbit hair, silk, hemp, pulp, etc. From the viewpoint of fiberlength necessary for intermingling property, wool and cotton arepreferred.

A weight of the web comprising PTFE staple fibers is preferably from 50to 500 g/m² from the points that inherent characteristics of PTFE can bemaintained and that there can be obtained effects such as frictionresistance in each application of the present invention and further costmerit, and is further preferably from 50 to 250 g/m² from the point thata uniform web can be obtained by a carding machine mentionedhereinafter.

When the weight of the web comprising PTFE staple fibers is decreased toas small as about 50 g/m² to about 100 g/m², a length of the staplefiber is preferably not more than 25 mm from the points that mixing offibers in web is good and a relatively uniform web can be obtained, morepreferably from 3 to 25 mm, further preferably from 3 to 20 mm,particularly preferably from 3 to 15 mm.

Such a short PTFE staple fiber can be obtained from a PTFE film by, forexample, a method comprising the sintering step, stretching step,splitting step, cutting step, etc. or a method comprising the sinteringstep or semi-sintering step, stretching step, tearing step and openingstep by a needle blade roll rotating at high speed, etc. or the likemethod.

When the joining step is carried out, for example, through water jetneedling mentioned later by using PTFE staple fibers having a shortlength, there is a problem that the fibers are easy to be scattered byhigh pressure water. The present inventors have found that the problemcan be solved when the PTFE staple fibers are previously subjected tohydrophilization before the joining step by the water jet needling.

Examples of the method for hydrophilizing PTFE staple fibers are, forinstance, a method disclosed in JP-B-5-21009 and JP-B-5-21010, in whichthe hydrophilization is carried out by surface-treating PTFE with anon-metallic ion type fluorine-containing surfactant and thencrosslinking until the surfactant becomes insoluble in an aqueousdispersion of ammonium salt of perfluoroalkylate so that the surfactantis not removed; a method disclosed in JP-A-4-249548, in which afluorine-containing compound having perfluoroalkyl group and hydrophilicgroup and the surface of PTFE are crosslinked with a compound having anisocyanate group to produce a hydrophilic fluorine-containing resinmaterial having a crosslinked structure; a method disclosed inJP-A-4-94724, in which the hydrophilization is carried out on thesurface of PTFE through sputtering and corona discharging; and the like.In the present invention, those methods can be used.

Example of the other method is a method of using a hydrophilic liquidhaving a surface tension of not more than 30 dyne/cm. When the surfacetension of the hydrophilic liquid is not more than 30 dyne/cm, ahydrophobic PTFE staple fiber easily gets wet. Examples of thehydrophilic liquid are, for instance, alcohols such as methanol, ethanoland isopropyl alcohol (IPA) and aqueous solutions of these alcohols.

Those methods for hydrophilizing are preferably carried out at anystages before the joining step by the water jet needling, for example,immediately after the PTFE film production step; immediately afteruniaxially stretching step of the film; immediately after tearing andopening step of the film or splitting and cutting step; or immediatelyafter placing the web comprising PTFE staple fibers on at least onesurface of the base felt mentioned later. Particularly in case of theuse of the above-mentioned hydrophilic liquid, it is preferable to dipinto the hydrophilic liquid immediately after placing the web from thepoint that the PTFE staple fibers are hardly scattered by the water jetneedling in the joining step following the web placing step. In additionto the dipping method, the hydrophilic liquid is used by coating,spraying, etc.

The multilayered felt of the present invention has such across-sectional structure as explanatorily described, for example, inFIG. 1(a). In FIG. 1(a), numeral 1 represents a layer (dense layer) of aweb comprising PTFE staple fibers formed on at least one surface of abase felt 2. The base felt 2 comprises a base fabric 3 in its centerregion and a fiber portion 4. FIG. 1(b) shows explanatorily thecross-section of the multilayered felt of the present invention shown inFIG. 1(a) after used as a filter cloth for dust collection as describedlater. Numerals 1 to 4 are the same as in above. Numeral 5 representsparticles of dusts.

The process for producing the multilayered felt of the present inventionis explained hereinbelow. Unless otherwise noted, each material used arethose mentioned above.

Production of Base Felt

(A) The base felt which can be used in the present invention is oneobtained from usual fibers by usual method, for example, by needlepunching, and commercially available felts can be used.

Examples of the base felt-forming fiber are, for instance, animal fiberssuch as wool; vegetable fibers such as cotton; inorganic fibers such ascarbon fiber and glass fiber; organic synthetic fibers such as polyesterfiber, meta-linked aramid fiber, para-linked aramid fiber, polyphenylenesulfide (PPS) fiber, polyimide fiber, phenol resin fiber,fluorine-containing resin fibers including sintered PTFE fiber andmolten spinning fiber such as tetrafluoroethylene-hexafluoropropylenecopolymer fiber, tetrafluoroethylene-pefluoro(alkyl vinyl ether)copolymer fiber or ethylene-tetrafluoroethylene copolymer fiber,polyolefin fibers such as polyethylene fiber and polypropylene fiber,acrylic fiber and nylon fiber, and the like. Among them, in case of afilter cloth for dust collection, one or a mixture of two or more ofpolyester fiber, meta-linked aramid fiber, para-linked aramid fiber,polyphenylene sulfide fiber, polyimide fiber, phenol resin fiber,fluorine-containing resin fiber, carbon fiber and glass fiber ispreferable.

It is preferable from the viewpoint of improvement of strength that thecenter region of the base felt comprises a base fabric such as aplain-woven fabric. Examples of the preferred fiber used for such a basefabric are the fibers mentioned above.

Production of Web to be Joined

(B) After stretched by 6 to 30 times, a semi-sintered PTFE film is tornand opened by a machine shown in FIG. 2.

In FIG. 2, numeral 6 represents a uniaxially stretched PTFE film,numeral 7 represents a pinch roll, numeral 8 represents a needle bladeroll, numeral 9 represents a needle, numeral 10 represents a hood,numeral 11 represents a transfer belt, numeral 12 represents an openedPTFE staple fiber and numeral 13 represents a cotton-like materialcomprising PTFE staple fibers.

The above-mentioned staple fiber obtained by tearing and opening has ashape as explanatorily shown in FIG. 3. In FIG. 3, numeral 14 representsa PTFE staple fiber constituting the cotton-like material, numeral 16represents a crimp, numerals 15, 17 and 18 represent branches andnumeral 19 represents a loop.

By such tearing and opening, there can be obtained a web which has aweight of 50 to 500 g/m² and comprises a cotton-like material of PTFEstaple fibers having loop structure and/or branch, being excellent incrimping property and having a length of 5 to 150 mm.

Production of Multilayered Felt

(C) The multilayered felt of the present invention can be obtained byplacing the web obtained in above (B) on the base felt shown in above(A) and then joining the felt-forming fibers and the web-forming staplefibers by intermingling them with a water jet needling machine. Examplesof the conditions for the water jet needling are those used for usualcotton fibers.

For producing the web comprising the semi-sintered PTFE staple fibers tobe joined to the base felt, it is preferable to use the tearing andopening machine shown in FIG. 2 from the point that there is neitherblocking nor depositing of the fibers in the machine. Also the use ofthe machine is further preferred because simplification of the steps canbe achieved since the fibers can be accumulated directly on the basefelt. Further in that case, the intermingling may be carried out withsuch a water jet needling machine as mentioned above after accumulatingthe staple fibers temporarily on a spun bond non-woven fabric or a wovenfabric having air permeability instead of the base felt and then placingon the base felt. By combination use of needle punching by metalneedles, the intermingling advances more and particularly the staplefibers are further intermingled with the fibers inside the base felt togive a strong multilayered felt.

Also by smoothing the surface of the layer comprising PTFE staple fibersof the multilayered felt obtained by the method mentioned above, thefelt having a lower friction coefficient and excellent mold releaseproperty can be obtained.

Means for surface smoothing may be one which can lower the frictioncoefficient and make the mold release property more excellent. Forexample, there may be used a continuous belt type laminator (forinstance, JR: 9005 available from Asahi Seni Kikai Kabushiki Kaisha)which has nip rolls being capable of heating and nipping by surfacepressure. Also a method for pressing successively with a heated iron maybe used, and an electric iron and a trouser press may be used. Degree ofsurface smoothness can be optionally changed by pressure or pressingtime at a temperature in the range of 100° to 360° C.

The multilayered felt obtained by the method mentioned above has thedense layer of the web comprising PTFE staple fibers in its surfaceregion. Since the fibers have loop structure and/or branch,intermingling property with the base felt-forming fibers is excellent.The staple fibers have particularly lower friction coefficient and haveelasticity and flexibility, and thus maintain characteristics which PTFEinherently possesses.

Those multilayered felts can be suitably used for, for example, filtercloth for dust collection, sliding member, water repellent member,non-sticking member, member for supplying mold releasing agent inelectrophotographic apparatuses, etc.

As the filter cloth for dust collection, the felt can be used, forexample, for a bag filter. The bag filter can be obtained, for example,by sewing the above-mentioned multilayered felt into the form of baghaving a diameter of 100 to 300 mm and a length of 0.5 to 5 m so thatthe PTFE staple fiber layer faces outside and then, inside the bag,inserting a shape holding frame called retainer. When a fluid (liquid orgas) containing particles such as dusts is supplied from the side of thePTFE staple fibers, the dusts are filtrated and the clean fluid can bereleased outside from an opening of the bag filter. Also the staplefiber layer may face inside of the filter. In that case, the fluid flowsreversely. Further in order to increase the filtrating area, themultilayered felt may be used in the form of pleat. Examples of thepreferred base felt-forming fibers of the bag filter are polyesterfiber, meta-linked aramid fiber, para-linked aramid fiber, polyphenylenesulfide fiber, polyimide fiber, phenol resin fiber, fluorine-containingresin fiber, carbon fiber or glass fiber or a mixture of two or morethereof.

Since the PTFE staple fibers are joined firmly by intermingling with thebase felt-forming fibers, when the multilayered felt is used for the bagfilter, a trouble of damaging the bag filter can be decreased becausethe felt is excellent in mechanical strength such as resistance toinflation, vibration, abrasion, etc. which are caused by pulse jet airor backwash air.

Also as a filter cloth for a heat resistant bag filter, there have beenwidely used a single layer felt comprising meta-linked aramid fiber, PPSfiber, polyimide fiber, PTFE fiber, or the like. On the other hand, thePTFE staple fiber has excellent characteristics, but is expensive.However, for example, by using a felt comprising only meta-linked aramidfiber as the base felt, and using the PTFE staple fibers only in thesurface region of the felt, the obtained multilayered felt is a filtercloth for a heat resistant bag filter which has combined merits ofexcellent characteristics of PTFE staple fibers and inexpensive basematerial.

Since the above-mentioned filter cloth for dust collection is composedof the layer of PTFE staple fibers on its dust-collecting surface, ithas excellent characteristics, namely a small surface energy. Thusparticles such as dusts are easily removed, for example, cohesion of wetdust does not occur and property for shaking down of dusts is excellent.

Also since the dense surface layer is formed of PTFE staple fibers,particles such as dusts do not enter deep into the base felt, andincrease in pressure loss can be maintained at a low level for a longperiod of time.

The above-mentioned sliding member can be produced by sticking the basefelt side of the multilayered felt to a plane portion, curved portion,folded portion, etc. of a member of, for example, metal, ceramic, glass,wood or plastic by using an adhesive. In this sliding member, thesurface of the PTFE staple fiber layer is used as sliding surface.

The sliding member is characterized in that it has both elasticity andflexibility of the base felt and low friction coefficient of the surfaceof the PTFE staple fiber layer. For example, in opening and closing of acurved window glass of cars, by using the sliding member on a windowframe, a clearance between the glass and the frame can be sealed and thewindow can be opened and closed by small force. Further the slidingmember can be used as a sliding surface contacting a rotating floppydisc and as a sliding surface of artificial skiing slope or playingslide.

Examples of the preferred base felt-forming fibers of the sliding memberare polyolefin fiber such as polyethylene fiber or polypropylene fiber,nylon fiber, polyester fiber and meta-linked aramid fiber.

The above-mentioned water repellent member is one obtained only bycutting the mentioned multilayered felt, one obtained by sewing a cutfelt so that the surface of the PTFE staple fiber layer becomes waterrepellent surface, one obtained by laminating the surface of the basefelt to cloth, wood, concrete wall, etc. with an adhesive irrespectiveof a cut or non-cut felt, or the like.

These water repellent members have elasticity, flexibility and airpermeability of the base felt, and are characterized in that they havepermanent water repellency as compared with application of a waterrepelling agent. The water repellent member obtained only by cutting themultilayered felt can be used for a table cloth, etc. and the memberobtained by sewing can be used for felt hat, gloves, rainwear, materialfor clothes, etc. Also by adhering the base felt side of themultilayered felt to building materials, the obtained materials can beused as wall materials, carpet etc.

Examples of the preferred base felt-forming fibers of these waterrepellent members are animal fiber such as wool, vegetable fiber such ascotton, nylon fiber, polyolefin fiber such as polyethylene fiber orpolypropylene fiber, polyester fiber and acrylic fiber.

The above-mentioned non-sticking member can be used for a non-stickingroll, for example, an elastic nip roll for a cloth or paper containingstarch, etc. which is produced by cutting the above-mentionedmultilayered felt into the form of ribbon and then adhering the basefelt side surface to a surface of a rolled material so that othersurface of the felt is non-sticking PTFE staple fiber layer. Also themultilayered felt cut can be processed and used for, for example, anironing stand. The ironing stand is necessary to pass steam through itand requires proper elasticity and it is required that cloth is notstuck to the ironing stand with starch. When the non-sticking member isused for such applications, good permeability of steam and non-stickingproperty for starch can be obtained, and since proper elasticity isavailable, ironing work is easy.

Examples of the preferred base felt-forming fibers of the non-stickingmembers are nylon fiber, polyester fiber, meta-linked aramid fiber andphenol resin fiber.

The member for supplying mold releasing agent in electrophotographicapparatuses is obtained by cutting the multilayered felt into the formof ribbon and winding the cut felt on a rolled material impregnated witha mold releasing agent, for example, silicone oil so that the PTFEstaple fiber layer becomes an outer surface, and thus can be used as amember which makes it possible to bleed the mold releasing agent slowlyonto the surface of the PTFE staple fiber layer and apply the moldreleasing agent to the surface of a heating roll or a press roll.Therefore toner offset can be prevented.

Examples of the preferred base felt-forming fiber of the member forsupplying mold releasing agent in electrophotographic apparatuses arepolyester fiber and meta-linked aramid fiber.

In the present invention, the above-mentioned multilayered felt can beused in the form of plate. For example, the multilayered felt of 500mm×500 mm may be framed with metal around its circumference and sealedso that liquid does not leak from the circumference. Also the both sidesof the multilayered felt may be covered with a net for reinforcement soas to resist to a pressure of the liquid. Further in order to increase afiltrating area, the multilayered felt in the form of pleat may be used.

When the multilayered felt of the present invention is used in the formof plate and particularly fluid is liquid, example of its application isa filter cloth for filter press. In that case, examples of the preferredbase felt-forming fiber are polyolefin fibers such as polyethylene fiberand polypropylene fiber, polyester fiber, polyimide fiber and PTFEfiber. When the PTFE fiber is used as the base felt, it is preferablethat the PTFE fiber is previously subjected to hydrophilization. Furtherwhen chemical resistance is particularly required, preferable arepolyimide fiber, PTFE fiber and carbon fiber.

In any cases mentioned above, it is preferable that the surface of thePTFE staple fibers of the filter cloth is brought into contact with thefluid containing particles such as dusts.

The present invention is then explained by means of Examples, but is notlimited to them.

EXAMPLE 1 AND COMPARATIVE EXAMPLES 1 to 2 Joining of Base FeltComprising PTFE Staple Fibers and Web Comprising PTFE Staple Fibers

Production of Base Felt

(1) The PTFE fine powder (POLYFLON F104 available from DaikinIndustries, Ltd.) was mixed with a liquid additive (IP2028 availablefrom Idemitsu Sekiyu Kagaku Kabushiki Kaisha), and then aging was doneat room temperature for two days and preforming was conducted bycompression to give a block. The preformed article in the form of blockwas paste-extruded and calendered, and then the additive was removed byheating and drying to make an unsintered film of 190 mm wide×60 μm.

(2) The unsintered film was heat-treated for 60 seconds in a saltsolution bath of 360° C., and a sintered film having a width of 165 mmand a thickness of 60 μm was obtained.

(3) The sintered film was stretched by 5 times in the longitudinaldirection by means of two rolls of 320° C. having different rotationspeeds, and thus a uniaxially stretched film of 110 mm wide×18 μm thickwas obtained.

(4) Then the uniaxially stretched film was split by means of a pair ofupper and lower needle blade rolls shown in FIG. 4. In FIG. 4, numeral20 represents the uniaxially stretched PTFE film, numerals 21 and 22represent the needle blade rolls and numerals 23 and 24 representneedles provided on the circumference of the needle blade roll.

The uniaxially stretched film 20 was split by means of a pair of upperand lower needle blade rolls 21 and 22 shown in FIG. 4 under theconditions of a feeding speed (v1) of the film 20 of 8 m/min, aperipheral speed (v2) of the needle blade rolls 21 and 22 of 64 m/minand a v2/v1 ratio of 8 times.

The shape of the needle blade rolls 21 and 22, and the arrangement andengagement of the needles 23 and 24 of the upper and lower needle bladerolls were as mentioned below. When the film 20 was passed at the samespeed as a rotation of the upper and lower needle blade rolls 21 and 22of FIG. 4, a punched film 25 as shown in FIG. 5 was obtained. In FIG. 5,A is a needle hole of the upper needle blade roll 21, and the pitch P1of the holes in the circumferential direction was 2.5 mm. B is a needlehole of the lower needle blade roll 22, and the pitch P2 thereof was 2.5mm just like P1. The number a of needles in the longitudinal directionof the roll was 13 per 1 cm. As shown in FIG. 6, the angle ( θ) of theneedle to the film 20 being fed between the needle blade rolls 21 and 22was so set as to be an acute angle (60°). As it is seen from FIG. 5, theupper and lower needle blade rolls were so set that the needles of theupper and lower needle blade rolls 21 and 22 were arranged alternatelyin the circumferential direction of the rolls. The length of the needleblade rolls in the longitudinal direction was 250 mm, and the diameterof the rolls was 50 mm at the ends of the needles.

(5) The split uniaxially stretched film was cut to 70 mm in thelongitudinal direction, and a cotton-like material can be produced byusing a carding machine (model SC360-DR available from Daiwa KikoKabushiki Kaisha) shown in FIG. 7. In FIG. 7, numeral 26 represents acotton mass conveyor, numeral 27 represents a drum, numeral 28represents a taker-in roller, numeral 29 represents a cylinder, numeral30 represents a doffer, numeral 31 represents a card crossing distanceand numeral 32 represents a cover. By passing the split uniaxiallystretched film through the carding machine, there was obtained acotton-like material which comprises the fibers (staple fibers) shown inFIG. 3 and having crimping property and at least one loop structureand/or branch per 5 cm.

An average diameter of the obtained fibers was measured by irradiatinglaser rays to the fibers and determining diameters of 2,000 fibersselected at random by using projections of the fibers with an automaticfiber diameter meter (FDA-200 available from Peyer Co., Ltd.). Theobtained average diameter was 29 μm.

(6) About 2% by weight of antistatic agent Elimina (available fromMaruzen Yuka Shoji Kabushiki Kaisha) was sprayed onto the obtainedcotton-like material, and then the material was passed through thecarding machine shown in FIG. 7 to give a web having a weight of 250g/m². At that time, the revolutions of the cylinder, doffer and drumwere 180 rpm, 6 rpm and 5 rpm, respectively.

(7) The obtained web was placed on a woven fabric (base fabric) ofCornex C01700 (available from Teijin, Ltd.) having a weight of 110 g/m².Further a web having a weight of 250 g/m² was produced in the samemanner as in (6) above, and placed on another surface of the basefabric. Then a needle-punched non-woven fabric (base felt) was producedby means of a needle punching machine (available from Daiwa KikoKabushiki Kaisha) with 750 needles/cm².

This base felt (weight: 610 g/m²) was used as a single felt ofComparative Example 1, and the base felt having a weight of 710 g/m² wasused as a single felt of Comparative Example 2. The multilayered felt ofExample 1 was, as mentioned below, a multilayered felt obtained byplacing, on the felt of Comparative Example 1, a web comprising PTFEstaple fibers and having a weight of 100 g/m² and then water jetneedling for intermingling.

Production of Web for Joining

(8) Then a semi-sintered film having a width of 170 mm and a thicknessof 60 μm was produced under the same conditions as in above (2) exceptthat the temperature was changed to 337° C. and the heat-treating timewas changed to 42 seconds.

(9) A stretched film having a width of 120 mm and a thickness of 20 μmwas produced by uniaxially stretching a semi-sintered film under thesame conditions as in above (3) except that the stretching ratio waschanged to 12.5 times and the temperature for stretching was changed to300° C .

(10) By employing the equipment for tearing and opening a uniaxiallystretched film as shown in FIG. 2, the uniaxially stretched PTFE film 6was torn and opened by means of the needle blade roll 8 rotating at highspeed. Thus a web 13 which was the same cotton-like material of staplefibers having a loop structure and/or a branch as shown in FIG. 3 wasproduced. A weight was 100 g/m² and an average diameter of the staplefibers was 21 μm.

The needle blade roll 8 shown in FIG. 2 differs from the needle bladeroll used in above (4) and has the structure mentioned below.

FIG. 8(a) is for explaining the needle blade roll 8 shown in FIG. 2. InFIG. 8(a), numerals 8 and 9 are the same as above. As shown in FIG.8(a), the needle blade roll 8 is a metal roll produced by dividing acylinder of 90 mm outside diameter×250 mm length into 90 parts on itscircumference and providing sharp needles 9 at intervals of 8 needlesper 1 cm in the longitudinal direction so that the outside diameter ofthe roll at the end of the needle is 100 mm. The rotational speed of theneedle blade roll 8 is 3,000 rpm and the film feeding speed is 2 m/min.FIG. 8(b) is a plan view of the needle blade roll shown in FIG. 8(a).

Production of Multilayered Felt

(11) The web produced in above (10) was placed on the base felt producedin above (7), and then the web-forming staple fibers and the basefelt-forming fibers were intermingled by means of a water jet needlingmachine (available from Perfojet Co., Ltd. (France)). Thus a joinednon-woven fabric (multilayered felt) of a two-layered structurecomprising a bulky layer obtained in above (7) and a dense layerobtained in above (10) was produced.

Such a two-layered structure can be seen by comparing state of enteringparticles in evaluations of performance mentioned later and airpermeability shown in Table 1.

Conditions for Water Jet Needling

The nozzles of the water jet needle were so arranged that 800 nozzleshaving 100 μm diameter were set at intervals of 0.6 mm in the transversedirection and at three rows in the longitudinal direction. The pressurewas 80 kg/cm², 120 kg/cm² and 170 kg/cm² at the first, second and thirdrows, respectively.

The following tests were carried out with respect to the multilayeredfelt obtained in Example 1 of the present invention and the multilayeredfelts obtained in Comparative Examples 1 and 2.

Air permeability: Measurement was carried out with a Frazier type airpermeability tester according to JIS L1096.

Pressure loss: Measurement was made at 3.3 cm/sec of a filtrating airvelocity by using an equipment shown in FIG. 9

Thickness: A thickness was measured by applying a load of 20 g/cm² byusing a compressive elasticity tester (available from Nakayama DenkiSangyo Kabushiki Kaisha). Measurement was made at 10 points selected atrandom and an average of them was used. The results are shown in Table1.

                                      TABLE 1                                     __________________________________________________________________________                          Layer of web                                                                  comprising                                                       Base felt    PTFE staple fibers                                      Structure                                                                              Weight                                                                            Number of needles                                                                      Weight                                                                            Intermingling                                                                        Thickness                                                                          Air permeability                                                                      Pressure loss                   of felt  (g/m.sup.2)                                                                       (per cm.sup.2)                                                                         (g/m.sup.2)                                                                       method (mm) (cc/cm.sup.2 /sec                                                                     (mm H.sub.2 O)                  __________________________________________________________________________    Ex. 1                                                                            Multilayered                                                                        610 750      100 Water jet                                                                            1.62 12.5    2.1                                felt                   needling                                            Com.                                                                             Single layer                                                                        610 750      --  --     1.78 34.3    0.8                             Ex. 1                                                                            felt                                                                       Com.                                                                             Single layer                                                                        710 750      --  --     1.91 26.2    1.4                             Ex. 2                                                                            felt                                                                       __________________________________________________________________________

As it is clear from the results of Table 1, increase in pressure loss ofthe multilayered felt of the present invention (Example 1) is within theallowable range.

Evaluation of Performance of Felt as Filter Cloth for Dust Collection

(12) Performance of each felt as a filter cloth for dust collectionwhich was obtained in Example 1 and Comparative Example 2 was evaluatedby using an equipment shown in FIG. 9.

In FIG. 9, numeral 33 represents a test filter (measuring area: 30 cm×30cm) produced from a multilayered felt or a single layer felt, numeral 34represents a nozzle for measuring pressure loss, numeral 35 represents amanometer, numeral 36 represents a dust feeder, numeral 37 represents apressure gauge, numeral 38 represents a header tank, numeral 39represents a solenoid valve, numeral 40 represents a valve, numeral 41represents a compressor, numeral 42 represents a nozzle for pulseinjection, numeral 43 represents a HEPA filter, numeral 44 represents anorifice, numeral 45 represents a blower, numeral 46 represents particlesof dusts (fly ash), numeral 47 represents a bag house proper and numeral48 represents particles of dusts not collected.

Dusts were supplied to a filter cloth under the following conditions.

Dusts: Fly ash d_(p50) 1.7 μm

Filtrating air velocity: 3.3 cm/sec

Fly ash concentration: 20 g/m³

Filtrating area: 30 cm×30 cm

Then every time when dusts 46 are accumulated and a differentialpressure before and after the test filter (filter cloth) 33 reaches 170mmH₂ O, particles of the accumulated dusts are shaken down by pulse airinjection (at a pressure of 3 kg/cm² for 0.1 second). Instantly afterthe shaking down, the differential pressure (pressure loss) before andafter the filter cloth decreases. The differential pressure immediatelyafter the shaking down usually increases as compared with the initialshaking down. The tendency of increase is shown in FIG. 10. In a graphof FIG. 10, numeral 49 represents a pressure loss when using a filtercloth produced from the multilayered felt obtained in Example 1 andnumeral 50 is a pressure loss when using a filter cloth produced fromthe felt obtained in Comparative Example 2. As a result, the pressureloss when using the filter cloth of Example 1 becomes constant afterabout ten times of pulse injections. As compared with that, with respectto the case of using the filter cloth of Comparative Example 2, thepressure loss after pulse injection continues increasing and in about 20times of pulse injections, reaches the same level of pressure loss asthat of the case of the filter cloth of Example 1. It is explicit from across-sectional view of the filter cloth as shown in FIG. 11 thatincrease in pressure loss is caused by the entering particles of dustsinto the filter cloth.

FIG. 11(a) is an explanatory cross-sectional view for explaining a stateof a filter cloth of Comparative Example 2 before dust collection. InFIG. 11(a), numeral 51 represents a base fabric, numeral 52 represents afiber portion of a base felt and numeral 53 represents the base felt.FIG. 11(b) is an explanatory cross-sectional view for explaining a stateof the filter cloth after dust collection. In FIG. 11(b), numerals 51,52 and 53 are the same as above. Numeral 54 represents particles ofdusts and numeral 55 represents particles of dusts passing through thefilter cloth.

As shown in FIG. 1(b), it is seen that the filter cloth of Example 1catches particles of dusts in a dense layer of its surface.

Thereby it is indicated that in case of the filter cloth of Example 1having a dense layer on its surface, even if an initial pressure loss issomewhat high, the pressure loss does not increase during use unlikeComparative Example 2.

Further in Comparative Example 2, as shown in FIG. 11(b), it wasobserved that during the tests, particles of dusts passed through thefilter cloth and leaked therefrom and that the surface of the filtercloth at the opposite side of the dust-collecting surface was stainedand colored. On the other hand, in case of the filter cloth of Example1, as shown in FIG. 1(b), stain at the opposite side of the filter clothwas not observed.

EXAMPLE 2 Joining of Base Felt of Fibers Other Than PTFE Staple Fibersand Web of PTFE Staple Fibers

Process for Joining into Multilayer

(1) As the base felt, there were used commercially available filterclothes for bag filter such as (a) filter material C09000 (trade name)comprising a meta-linked aramid fiber and being available from Teijin,Ltd. (this material has a dust-collecting surface subjected to singeing)and (b) filter material P84 (trade name) comprising a polyimide fiberand being available from Lenzing Co., Ltd. (this material has adust-collecting surface subjected to singeing).

Joining of a web of PTFE staple fibers and the above-mentioned two kindsof base felts was carried out on the surface opposite to thedust-collecting surface of the base felt by the methods of (8), (9),(10) and (11) of Example 1, thus producing a multilayered felt (c) withabove (a) and a multilayered felt (d) with above (b).

Further (c) was nipped (nip pressure: 5 kg/cm, peripheral speed: 2m/min) from above with a silicone rubber roll by bringing the PTFEsurface into contact to a metal roll surface heated to 200° C. to makethe surface of PTFE layer smooth, and thus a multilayered felt (e)having a smoothed PTFE surface was produced. Also a multilayered felt(f) having a smoothed PTFE surface was produced from the multilayeredfelt (d). Weight, thickness and air permeability of above (a) to (f)were measured in the same manner as in Example 1, and shown in Table 2.A weight of PTFE was 100 g/m².

With respect to above (c) to (f), peel test was carried out by using anadhesive tape VINYCLOTH (trade name) available from Sekisui KagakuKabushiki Kaisha to check to see occurrence of interface adhesionfailure between the layer of PTFE staple fibers and the base felt. Thereoccurred no peeling between them.

Though removal of fibers was observed on the surface of the adhesivetape slightly, its amount was less than 5% (based on filter material)per one application of the tape through weight method.

With respect to a commercially available filter material produced bylaminating an expanded porous membrane to a glass cloth, when the samepeel test as above was conducted, interface adhesion failure occurredeasily. (Performance test of filter cloth for dust collection) (2)Performance test of above (a) to (f) as the filter cloth for dustcollection was carried out under the same conditions as in above (12).

The dust-collecting surfaces of (a) and (b) were surfaces not subjectedto singeing, and the dust-collecting surfaces of (c), (d), (e) and (f)were PTFE layer surface.

The dust collection and shaking down by pulse injection were repeated 20times, and the results thereof are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                            Pressure loss.sup.1)                                                    Air   (mm H.sub.2 O)                                                                permea- Initial                                                                            Immedi-                                                  Thick-  bility  pulse                                                                              ately after                                  Weight      ness    (cc/cm.sup.2 /                                                                        injec-                                                                             20th pulse                                                                           Friction.sup.2)                       (g/m.sup.2) (mm)    sec)    tion injection                                                                            coefficient                           ______________________________________                                        Kind of                                                                             a     450     2.0   26    3.2  12     0.26                              felt in                                                                             b     500     2.4   20    4.1  14     0.29                              Ex. 2 c     550     2.2   17    5.1  10     0.20                                    d     600     2.6   12    6.0  11     0.20                                    e     550     2.0   10    9.2  13     0.18                                    f     600     2.4    8    10.7 15     0.18                              Kind of                                                                             i     550     2.2   17    5.2  10     0.20                              felt in                                                                             j     550     2.0   10    9.3  13     0.18                              Ex. 3                                                                         ______________________________________                                         .sup.1) Air velocity when measuring a pressure loss is 3.3 cm/sec.            .sup.2) FEM4S (available from Toyo Sokki Kabushiki Kaisha) was used as a      friction coefficient measuring equipment. Namely a force f for pulling a      steel ball having a weight (w) of 200 g at a speed of 0.27 cm/sec is          measured, and a friction coefficient μ is calculated by an equation of     μ = f/w.                                                              

As it is clear from the results of Table 2, ratios of increase inpressure loss immediately after the pulse injection of (c), (d), (e) and(f) were smaller than those of (a) and (b).

As a result of the observation, the reason of difference in change ofthe ratio of increase is that like above (12), in (a) and (b), dustswere entering from the surface deeply into the base fabric and that in(c), (d), (e) and (f), dusts were caught by a layer comprising PTFEstaple fibers and hardly entered into the base felt.

Performance Test as a Sliding Member

(3) Friction coefficients of the surfaces of (a) and (b) in (1) ofExample 2 which had not been subjected to singeing and the surfaces oflayers of the multilayered felts (c), (d), (e) and (f) which comprisedPTFE staple fibers were measured by the method mentioned below Table 2.The results are shown in Table 2.

As it is clear from the results of (c), (d), (e) and (f) of Table 2,friction coefficients thereof could be decreased largely as comparedwith those of (a) and (b).

Further the surface of above (c) was smoothed by COMFIT (trade name)available from Uenoyama Kiko Kabushiki Kaisha (peripheral speed of roll:1 m/min, temperature: 140° C. ) to give a multilayered felt (g). As aresult, the friction coefficient of the surface of a layer of PTFEstaple fibers could be decreased up to 0.15.

Further the multilayered felt (d) was subjected to smoothing by pressingby hand a metal plate heated to 360° C. to the surface of a layer ofPTFE staple fibers of the felt (d), and thus a multilayered felt (h) wasobtained. The friction coefficient of the PTFE surface could bedecreased to 0.13.

Mold Release Property Test

(4) With respect to (g) and (h) obtained in (3) of Example 2, peel testwas repeated on the surface of a layer of PTFE staple fibers by using anadhesive tape. There was no removal of staple fibers, and there was notransfer of an adhesive onto the surface.

On the other hand, with respect to above (a) and (b), peel test wascarried out by using the adhesive tape, and there occurred removal offibers and raising of fibers.

Water Repellency Test

(5) With respect to the both surfaces of commercially available (a) and(b) and the surfaces of web layers of PTFE staple fibers of (c), (d),(e), (f), (g) and (h) of Example 2, water repellency of the surfaces wasobserved by using a mixed solution of IPA (isopropyl alcohol) and water.The water repellency was evaluated as ◯ when the mixed solution wasrepelled, and as × when the mixed solution infiltrated through thesurface. The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Mixing ratio of IPA/water in mixed solution (weight ratio)                    50/50        40/60    30/70    20/80  0/100                                   ______________________________________                                        Kind of                                                                             a     X        X      X      X      X                                   felt in                                                                             b     X        X      X      X      X                                   Ex. 2 c     X        X      ◯                                                                        ◯                                                                        ◯                             d     X        X      ◯                                                                        ◯                                                                        ◯                             g     X        X      ◯                                                                        ◯                                                                        ◯                             e     X        X      ◯                                                                        ◯                                                                        ◯                             f     X        X      ◯                                                                        ◯                                                                        ◯                             h     X        X      ◯                                                                        ◯                                                                        ◯                       Kind of                                                                             i     X        X      ◯                                                                        ◯                                                                        ◯                       felt in                                                                             j     X        X      ◯                                                                        ◯                                                                        ◯                       Ex. 3                                                                         ______________________________________                                    

As is clear from the results of Table 3, it is seen that with respect tothe multilayered felts (c), (d), (e), (f), (g) and (h) of the presentinvention obtained in Example 2, the surfaces of the hydrophilic feltshad been modified to strong hydrophobic surfaces.

EXAMPLE 3 Tearing and Opening a Uniaxially Stretched PTFE Film WithNeedle Blade Roll Rotating at High Speed to Give Staple Fibers, at theSame Time, Accumulating the Staple Fibers Directly on Base Felt and ThenIntermingling by Water Jet Needling to Prepare a Multilayered Felt

Placing of Web

(1) FIG. 12 is an explanatory cross-sectional view of an equipment usedin Example 3 for tearing and opening a PTFE film, accumulating on a basefelt and then intermingling. In FIG. 12, numerals 6 to 9, 12 and 13 arethe same as above, numeral 57 represents a blower, numeral 58 representsan air flow, numeral 59 represents a transfer belt, numeral 60represents a base felt, numeral 61 represents a water jet needlingmachine, numeral 62 represents a high pressure water flow from the waterjet needling machine and numeral 63 represents a multilayered felt.

First the same staple fiber 12 having loop structure and/or branch asthe staple fiber shown in FIG. 3 was produced by tearing and opening theuniaxially stretched PTFE film 6 obtained in (8) and (9) of Example 1,with the needle blade roll 8 rotating at high speed in the equipmentshown in FIG. 12. At the same time, the obtained staple fibers 12 wereaccumulated on the base felt 60 conveyed by the transfer belt 59 shownin FIG. 12 so that the web 13 having a weight of 100 g/m² was obtained.In that case, the web 13 was drawn by the blower 57. As the base felt60, there was used a filter material CO9000 (trade name) of meta-linkedaramid fiber available from Teijin, Ltd., which is a commerciallyavailable filter cloth for bag filter. An average diameter of the PTFEstaple fibers 12 was 21 μm.

The needle blade roll 8 shown in FIG. 12 differs from the needle bladeroll used in (4) of Example 1 and has the structure mentioned below.

Namely as shown in FIG. 8(a), the needle blade roll 8 is a metal rollproduced by dividing a cylinder of 90 mm outside diameter×250 mm lengthinto 90 parts on its circumference and providing sharp needles 9 atintervals of 8 needles per 1 cm in the longitudinal direction so thatthe outside diameter of the roll at the end of the needle is 100 mm. Therotational speed of the needle blade roll 8 was 3,000 rpm and the filmfeeding speed was 2 m/min.

Process for Joining Into Multilayer

(2) Next the base felt 60 produced in (1) of Example 3, on which thePTFE staple fibers 12 were placed, was subjected to water jet needlingwith the water jet needling machine 61 (available from Perfojet Co.,Ltd. (France)) shown in FIG. 12 to intermingle the staple fibers formingthe web 13 and the fibers forming the base felt 60. Thus a multilayeredfelt 63 (hereinafter referred to as "(i)") of a two-layered structurecomprising the base felt layer and the PTFE staple fiber layer wasproduced.

Conditions for Water Jet Needling

The nozzles of the water jet needle were so arranged that 800 nozzleshaving 100 μm diameter were set at intervals of 0.6 mm in the transversedirection and at three rows in the longitudinal direction. The injectionpressure was 80 kg/cm², 120 kg/cm² and 170 kg/cm² at the first, secondand third rows, respectively.

Further while bringing the PTFE surface of above (i) into contact with ametal roll surface heated to 200° C., (i) was nipped from above withsilicone rubber rolls (nip pressure: 5 kg/cm, peripheral speed: 2 m/min)to smooth the PTFE surface. Thus a multilayered felt (j) was produced.

Weight, thickness and air permeability of above (i) and (j) weremeasured in the same manner as in Examples 1 and 2. The results areshown in Table 2.

With respect to above (i) and (j), peel test was carried out by using anadhesive tape VINYCLOTH available from Sekisui Kagaku Kabushiki Kaishato check to see occurrence of interface adhesion failure between thelayer of PTFE staple fibers and the base felt. There occurred no peelingbetween them.

Though removal of fibers was observed on the surface of the adhesivetape slightly, its amount was less than 5% (based on filter material)per one application of the tape through weight method.

With respect to a commercially available filter material produced bylaminating an expanded porous membrane to a glass cloth, when the samepeel test as above was conducted, interface adhesion failure occurredeasily. (Performance test of filter cloth for dust collection) (3)Evaluation of performance of above (i) and (j) as a filter cloth fordust collection was carried out under the same conditions and in thesame manner as in Examples 1 and 2. A dust-collecting surface was a PTFEsurface. The results of repeating dust collection and shaking down ofdusts by pulse injection by 20 times are shown in Table 2. As it isclear from the results of Table 2, in (i) and (j), a ratio of increasein pressure loss immediately after the pulse injection was smaller ascompared with above (a) and (b).

As a result of the observation, the reason of a difference in change ofthe ratio of increase was that like Examples 1 and 2, in (a) and (b),dusts were entering from the surface deeply into the base fabric andthat in (i) and (j), dusts were caught by a layer comprising PTFE staplefibers and hardly entered into the base felt.

Performance Test as a Sliding Member

(4) Friction coefficients of the PTFE surfaces of (i) and (j) weremeasured. The results are shown in Table 2.

As it is clear from the results of Table 2, friction coefficients of (i)and (j) could be decreased largely like above (c) and (e) as comparedwith those of (a) and (b).

Water Repellency Test

(5) With respect to the PTFE surfaces of (i) and (j) of Example 3, waterrepellency of the surfaces was observed by using a mixed solution of IPA(isopropyl alcohol) and water. The water repellency was evaluated as ◯when the mixed solution was repelled, and as × when the mixed solutioninfiltrated through the surface. The results are shown in Table 3.

From Table 3, it is seen that with respect to (i) and (j) obtained inExample 3, the surfaces of the hydrophilic felts had been modified tostrong hydrophobic surfaces.

EXAMPLE 4

(1) Placing of a web was carried out in the same manner as in (1) ofExample 3 except that a weight of the web of PTFE staple fibers placedon a base felt which was a filter material C09000 (trade name) ofmeta-linked aramid fiber being commercially available from Teijin, Ltd.as a filter cloth for bag filter was changed to 50 g/m².

(2) With respect to the base felt produced in (1) of Example 4, on whichthe web was placed, the layer of PTFE staple fibers thereof was wetted(hereinafter referred to as "pre-wet") with IPA and water jet needlingwas carried out with the water jet needling machine (available fromPerfojet Co., Ltd. (France)) shown in FIG. 12 to intermingle the staplefibers forming the web and the fibers forming the base felt. Thus amultilayered felt (k) of a two-layered structure comprising the basefelt layer and the PTFE staple fiber layer was produced.

Conditions for Water Jet Needling

The nozzles of water jet needle were so arranged that 800 nozzles having100 μm diameter were set at intervals of 0.6 mm in the transversedirection and at three rows in the longitudinal direction. The pressurewas 40 kg/cm², 80 kg/cm² and 130 kg/cm² at the first, second and thirdrows, respectively.

The pre-wetting is usually carried out with water. However since PTFE ishydrophobic and is not get wet with water, IPA was used to reduce asurface tension. Any other one which decreases a surface tension may beused.

In the obtained multilayered felt (k), the PTFE staple fibersaccumulated on the base felt could be intermingled with the fibers ofthe base felt without damaging appearance of the web obtained in (1) ofExample 4, that is, with the mixing of fibers of the web being as itwas.

COMPARATIVE EXAMPLE 3

(1) After the felt obtained by placing a web on the base felt which wasproduced in (1) of Example 3 was subjected to pre-wetting with water,water jet needling was carried out with the water jet needling machine(available from Perfojet Co., Ltd. (France)) shown in FIG. 12 tointermingle the staple fibers forming the web and the fibers forming thebase felt. Thus a multilayered felt (m) of a two-layered structurecomprising the base felt layer and the PTFE staple fiber layer wasproduced. (Conditions for water jet needling).

The water jet needling was carried out in the same manner as in Example3.

In the obtained multilayered felt (m), mixing of fibers of the webobtained in (1) of Comparative Example 3 by accumulating the PTFE staplefibers on the base felt was remarkably damaged. In other words,intermingling with the base felt could not be done with the web being asit was. The PTFE staple fibers of the web were scattered by waterpressure of water jet needling.

INDUSTRIAL APPLICABILITY

The filter cloth for dust collection of the present invention assuressmall pressure loss and easy shaking down of dust particles, and isexcellent in friction property and mechanical strength.

Also the sliding member of the present invention is excellent in slidingproperty.

Also the water repellent member of the present invention is excellent inwater repellency.

Also the non-sticking member of the present invention is excellent innon-sticking property.

Also the member for supplying mold releasing agent inelectrophotographic apparatuses is excellent in air permeability, heatresistance and oil resistance.

Further the present invention can provide the multilayered felt whichcan be used for these members and the process for producing themultilayered felt.

What is claimed is:
 1. A multilayered felt obtained by forming a layerof a web comprising polytetrafluoroethylene staple fibers on at leastone surface of a felt and joining the polytetrafluoroethylene staplefibers and fibers which form the felt by intermingling,wherein thepolytetrafluoroethylene staple fibers have a branch and/or a loop. 2.The multilayered felt of claim 1, wherein a length of thepolytetrafluoroethylene staple fiber is from 3 to 25 mm.
 3. Themultilayered felt of any of claims 1, wherein thepolytetrafluoroethylene comprises a semi-sinteredpolytetrafluoroethylene.
 4. The multilayered felt of any of claims 1,wherein a weight of the web comprising the polytetrafluoroethylenestaple fibers is from 50 to 500 g/m².
 5. A filter cloth for dustcollection comprising a multilayerd felt obtained by forming a layer ofa web comprising polyterafluoroethylene staple fibers on at least onesurface of a felt and joining the polytetrafluoroethylene stable fibersand fibers which form the felt by intermingling.
 6. The filter cloth fordust collection of claim 5, wherein the fibers which form the felt areat least one selected from the group consisting of polyester fibers,meta-linked aramid fibers, para-linked aramid fibers, polyphenylenesulfide fibers, polyimide fibers, phenol resin fibers,fluorine-containing resin fibers, carbon fibers or glass fibers.
 7. Aprocess for producing a multilayered felt by placing a web ofpolytetrafluoroethylene staple fibers having a branch and/or a loop, onat least one surface of a felt and then joining thepolytetrafluoroethylene staple fibers and the fibers which form the feltby intermingling through water jet needling and/or needle punching. 8.The process for producing a multilayered felt of claim 7, wherein thepolytetrafluoroethylene staple fibers are obtained by tearing andopening a uniaxially stretched polytetrafluoroethylene film with aneedle blade roll rotating at high speed and immediately after theopening, the polytetrafluoroethylene staple fibers are accumulated onthe felt to be joined to form the web.
 9. The process for producing amultilayered felt of claim 7, wherein the polytetrafluoroethylene staplefibers which form the web are previously subjected to hydrophilizationand immediately after the opening, the polytetrafluoroethylene staplefibers are accumulated on the felt to be joined to form the web.
 10. Theprocess for producing a multilayered felt of claim 7, wherein the web isjoined to the felt after being subjected to hydrophilization.
 11. Theprocess for producing a multilayered felt of claim 10, wherein the webis subjected to hydrophilization with a hydrophilic liquid having asurface tension of not more than 30 dyne/cm.
 12. The process forproducing a multilayered felt of claim 7, wherein thepolytetrafluoroethylene comprises a semi-sinteredpolytetrafluoroethylene.